(19)
(11) EP 1 220 152 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
24.11.2004 Bulletin 2004/48

(43) Date of publication A2:
03.07.2002 Bulletin 2002/27

(21) Application number: 01310111.8

(22) Date of filing: 03.12.2001
(51) International Patent Classification (IPC)7: G06T 1/00
(84) Designated Contracting States:
AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE TR
Designated Extension States:
AL LT LV MK RO SI

(30) Priority: 07.12.2000 GB 0029865
07.12.2000 GB 0029869

(71) Applicant: SONY UNITED KINGDOM LIMITED
Weybridge KT13 0XW (GB)

(72) Inventors:
  • Pelly, Jason Charles
    Reading, Berkshire RG6 4DU (GB)
  • Tapson, Daniel
    Basingstoke, Hampshire RG21 3PL (GB)
  • Keating, Stephen Mark
    Reading, Berkshire RG6 3AB (GB)

(74) Representative: Pratt, Richard Wilson et al
D Young & Co 120 Holborn
London EC1N 2DY
London EC1N 2DY (GB)

   


(54) Embedding data in material


(57) A spatial domain image I produced by a source 1 is combined with watermark data Ri to produce a spatial domain watermarked image I'. The watermarked image is produced by an embedder 3 according to the equationCi'=Ci + α. Ri
  • where Ci and Ci' are wavelet transform coefficients of the image, and α is a scaling factor, α is chosen so that the watermark is imperceptible in the image and to resist removal of the watermark by unauthorised processing. It is desirable that α has the smallest value which achieves that. If α is too big the watermark is perceptible in the image; if it is too small the mark may not survive processing of the image.
  • α is determined from a trial decoding of the image I in a decoder 4. The decoding is that which would be used to decode the watermarked image I'. A value α' is produced by a calculator S3-S8, to which an offset value is added by an adder S9 to produce α. This produces values of α over the image, which are used to scale the data Ri so as to conceal the data. An image is one example of material to which the invention is applicable.

The step of producing modified coefficient values Ci may not use coefficients of magnitude greater than a threshold T and does not use corresponding information symbols Ri. Alternatively, a threshold Tclip may be set. The scaling factor α is calculated using clipped coefficient values and coefficients Ci of magnitude less than Tclip.






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